I really do not think that a lot of people are doing as what you are saying. Specially the big holders or the ones that are working hard for their possessions. I just can't get myself to see such a scenario. Maybe for some, because they only have small amounts and want to day trade with those bitcoins. But other than that? I really cannot see any reason good enough to make someone do this. The most common thing I see is people doing both for varied purposes. But if there really are people that are doing this with huge funds, and just leave their funds sit on an exchange, they are either rich as fck or on a whole new level of stupidity.